But, independent of these two causes, we presume, that the desire of obtaining a safe breeding place is likewise in timately connected with the movements of many species. " Of the vast variety of water fowl," says Pennant, "that frequent Great Britain, it is amazing to reflect how few are known to breed here : the cause that principally urges them to leave this country, seems to be not merely the want of food, but the desire of a secure retreat. Our country is too populous for birds so shy and timid as the bulk of these are. When great part of our island was a mere waste, a tract of woods and fens, doubtless many spe cies of birds (which at this time migrate) remained in se curity throughout the year. Egrets, a species of heron, now scarce known in this island, were in former times in prodigious plenty ; and the Crane, that has totally forsaken this country, bred familiarly in our marshes, their place of incubation, as well as of all other cloven footed waterfowl (the heron excepted) being on the ground, and exposed to every one. As total economy increased in this country, these animals were more and more disturbed ; at length, by a series of alarms, they were necessitated to seek, during the summer, some lonely safe habitation. On the contra ry, those that build or lay in the most inaccessible rocks that impend over the British seas, breed there still in vast numbers, having little to fear from the approach of man kind ; the only disturbance they meet with, in general, be ing from the desperate attempts of some few to get their eggs." It happens, in consequence of this desire of safety during incubation, that. the same species may be stationary at one place, while it is migratory at another. Thus, in the Western Islands, the common plover is stationary, while an the Grampians it is migratory. Herons may be met with along all the British shores during the winter season, while they are found congregated to breed in but fcw places. The turnstone is migratory in England, but stationary in the northern islands of Scotland. The same remark is ap plicable to the hooded crow, a few of which pass from us during the winter months into England, but return during the breeding season.
None of these causes, taken singly, may be able to ac count for the migrations of the feathered race ; but, when viewed in connection, they seem to include all those proxi mate causes which operate in the production of these curi rious, and to us in some respects useful voyages. These migrations extend our knowledge of birds, by making us acquainted with the productions of the shores oF Greenland, the mountains of Norway, and the marshes of Lapland. They also contribute to enliven the scenes of winter, and occasionally add to the delicacies of our table ; while, in their movements, we discern the marks of benevolence in preserving their existence, increasing their happiness, and extending their usefulness.
We cannot dismiss this subject of migration without re commending it to the attentive consideration of our readers.
To those who pass their time in the sweets of retirement in the country, it will prove a never-failing source of amusement ; and to a reflecting mind, will yield no small portion of delight. The field of observation is extensive, the subject curious. Quis non cum admiratione videat ordinem et polititiam peregrinantium avium, In itinere, tur matim volantium, per longos tcrrarum et marls tractus ab sque acu marina.—Quis eas certum iter in aeris mutabili regione docuit ?• Quis preteritte signa, et futurm vitt indi cia ? Quis eas ducet, nutrit, et vita? necessaria ministrat ? insulas et hospitia illa, in quibus victum reperiat, in dicavit, modumque ejusmodi loca in peregrinationibus suis inveniendi ? Hme sane superant hominum captum et in dustriam, qui non nisi longis experientiis, muftis itinerariis, chartis geographicis—ct acus magnetic beneficio—ejus modi rnarium et terrarum tractus conficere tentant, et au 'lent." As we descend in the scale of being, the instances of ac tual migration diminish in number. The locomotive pow ers of these animals, are too limited to enable them to un dertake extensive journies, and when necessary to be pro tected from the cold of winter, nature employs, with re spect to them, a more simple process, by subjecting them to a temporary lethargy. This is the case with reptiles, which present no instances of migration.
The migrations of fishes have long been the subject of !teen discussion among naturalists. An agreement of opin ion, however, has not been produced, although many obser vations have been published on the subject. Many of these observations, we fear, are the result of prejudiced inquiry, and ought therefore to be received with caution.
The movements of fishes are not performed with the same regularity and precision as the migrations of the fea thered tribes. Shoals of haddocks, for example, frequent for several years a particular part of the coast, and, with out any apparent cause, take their departure, accompanied with all those animals which feed on them. The move ments of those fish which approach our shores, for the pur pose of depositing their spawn, are more regularly perform ed. But these migrations can scarcely be considered as instances of hybernation. They have but little relation to the seasons of the year, as the fry of these fish may be found in almost every season in our rivers, and as their move ments are known to depend on their condition with respect to fecundation. In our article ICHTHYOLOGY, a par ticnlar account will be given of the migratory movements of the different species of British fishes.
Among the illollusca, Cirrhipcdes, and Annelides, no examples of a migrating hybernation have occurred. In the class Crustacea there is one very curious instance of migration, which the reader will find given in detail under the species Ocypodc uca.